With the development of film formation techniques in recent years, various materials and devices are becoming constructed mainly of thin films of 1 μm or thinner. Lately, high-speed film-formation techniques have been developed, which enable formation of a thin film structure by holding plural functional films on a substrate as a fine part of high functionality, such as electronic devices and bio-chips. Further, thin film structures having a sensor function, which detect a micro quantity of a chemical reaction product by utilizing plural components in the thin film, have become important.
With such improvements of the function of thin film parts, methods are being developed for more precise and finer analysis and evaluation of the thin films. The examples of the methods are:
(1) Direct measurement of electroconductivity, hardness, optical properties, X-ray reactivity, and ionic reactivity for measurement of functions of a thin film;
(2) Indirect analysis of the components of a thin film by fractionation of a thin film component by gas chromatography, high-speed liquid chromatography, ICP-MS analysis, or a like method;
(3) Marker insertion to an objective substance in the thin film, such as addition of a fluorescent functional substance, or substitution by an isotopic element;
and combinations thereof.
In particular, precise and accurate analysis of the film components is indispensable, because the functions of the thin film are affected delicately by the component ratios. The extremely small thickness of the thin film tends to cause a problem of dependence of the functions of the thin film on the state of the substrate for the thin film and a problem of an adverse effect of contamination with foreign matter or a change of the quality or quantity of the thin film by pretreatment. The dependence of the function of the thin film on the film component ratio is investigated frequently by formation of thin film samples constituted of various component concentration ratios, direct measurement of the function as mentioned in the above method (1), and preparation of a calibration curve regarding the dependency of the obtained signal intensity on the component concentration ratio. For preparation of a more accurate calibration curve, the components should be uniformly distributed in the thin film sample and there must be precise control of the component concentration ratio in the samples.
P. Lazzeri et al. (Surface and Interface Analysis, Vol. 29, 798 (2000)) describes formation of a thin film by spin coating and analysis thereof with a time-of-flight secondary ion mass spectrometer (hereinafter referred to as a “TOF-SIMS”). In this method, the size of one thin film is several millimeters square. This size is about ten thousand times the size of thin films used currently in devices in which the size of the one thin film is being decreased to tens of micrometers square. Such a large difference in the size causes a difference between the practical thin films and the thin films for calibration samples due to local flocculation and mixing state of the respective components, and other conditions. Therefore, ideally, the entire thin film is to be measured and analyzed at one time. However, one measurement region of the TOF-SIMS is as small as several hundreds of micrometers square, which cannot cover the entire thin film at once. Therefore, the measurement sectional regions are introduced successively into a measurement chamber for the measurement. In such a measurement process, during the waiting time for the measurement, the component ratio is liable to vary by adhesion of moisture or an impurity from the environmental atmosphere to the measurement regions or evaporation of the sample component from the measurement regions.
(1) Direct measurement of electrical conductivity, hardness, optical properties, X-ray reactivity, and ion reactivity as the thin film functionality.
Energy dispersive fluorescent X-ray analysis is capable of a simultaneous measurement of Na and heavier elements by use of a fluorescent X-ray. The fluorescent X-ray intensities are proportional in first approximation to the concentrations of the respective elements, but are affected greatly by ratio of coexisting component elements by absorption and secondary excitation effect thereof. Therefore, in the fluorescent X-ray analysis, the standard specimens for the calibration should also be prepared by strictly controlling the component mixing ratio for the quantitative determination of the film components and evaluating the functionality.
U.S. Pat. No. 5,365,563 evaluates the influence of the component mixing ratio in the thin film by a calculation in a quantitative determination by fluorescent X-ray measurement. In this method, however, precise calculation is difficult, because the fluorescent X-ray intensity is not necessarily in a linear relationship with the component ratio. Further, in this method, the samples should be prepared in a number corresponding to the number of the film components, which requires finally tested specimens of high accuracy for the quantitative determination.
Due to the above reasons, precise quantitative determination is not practicable in any of the conventional methods. Therefore, in many analysis methods including ionic analysis and fluorescent X-ray analysis, standard specimens should be prepared with accurate and precise control of the component concentration ratio.